We request support of our studies on the role of Epstein-Barr virus (EBV) in tumor promotion. We postulated that EBV functions as a tumor promoter by inducing uncontrolled proliferation of chemically- or otherwise - initiated cells, thereby allowing selection of neoplastic cells. To study this function of EBV, we have developed new experimental model systems in which the interaction between EBV and target cells in vitro is separated into two pathways: a) the cell-transformation pathway (related to the process of tumor promotion in vivo), and b) the non-transforming (lytic) pathway (unrelated to tumorigenesis). Using these model in vitro systems, we began to test our working hypothesis that the role of EBV in carcinogenesis involves a virally-induced increase in viral and/or cellular gene product(s) that block(s) viral lytic cycle and activate(s) the mechanisms responsible for cell transformation. We have found that EBV-induced nuclear antigen EBNA-1 may play a role in suppression of the viral lytic cycle. We have also shown that the other nuclear antigen, EBNA-2, may induce cell proliferation. Finally, we have demonstrated that some chemical carcinogens, such as benzo(a)pyrene, act synergistically with EBV in the process of stimulating cell growth. The goal is to continue and to extend our studies on the molecular mechanism of cell transformation by EBV and role of chemical carcinogens in the process. Specifically, we propose: 1) Study expression of EBV regulatory and transformation-related functions following infection of new host cells with the virus; 2) Identify EBV subgenomic fragments containing the regulatory genes; and 3) Continue our attempts to modify the virus-cell interaction, in order to determine the role of chemical carcinogens and cellular transforming genes as cofactors in EBV-induced cell transformation. New methods, such as recombinant DNA, Southern, Northern and dot-blotting and nucleic acid hybridization, Western blotting, and others, will be utilized in this project, together with previously-established procedures of EBV receptor-implantation and RSVE-mediated gene transfer. The proposed studies will help to elucidate the role of EBV in the multi-step process of carcinogenesis.